1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical elastic mount capable of damping and/or isolating vibrations applied thereto, based on flows of a fluid contained therein. More particularly, the invention is concerned with such a fluid-filled elastic mount capable of exhibiting sufficient damping and/or isolating characteristics with respect to the vibrations applied in any radial direction perpendicular to the axis of the mount.
2. Discussion of the Prior Art
A cylindrical elastic mount is known as a device for elastically or flexibly connecting two members in a vibration system in a vibration damping or isolating manner. Examples of such a cylindrical elastic mount are disclosed in laid-open Publication No. 48-310 of examined Japanese Utility Model Application and British Patent No. 1063863. The cylindrical elastic mount disclosed therein has an inner and an outer sleeve which are made of a metallic material and are disposed in radially spaced-apart relation with each other. Between these inner and outer sleeves, there is interposed an elastic body for elastically connecting the two sleeves. The thus constructed elastic mount is adapted to damp and/or isolate vibrations which are applied between the inner and outer sleeves primarily in radial directions perpendicular to the axis of the mount. This type of cylindrical elastic mount is widely used as a differential mount, engine mount, body mount or suspension bushing for a motor vehicle, for example.
To meet increasing requirements for a higher degree of vibration damping capability, a so-called fluid-filled mount has been recently proposed, as disclosed in Publication Nos. 48-36151 and 52-16554 of examined Japanese Patent Applications. A fluid-filled elastic mount as disclosed in these publications has two fluid chambers which are formed between the inner and outer sleeves, and are disposed opposite to each other in a radial direction of the mount. The two fluid chambers are held in fluid communication with each other through a suitable orifice passage, so that applied vibrations may be effectively damped by resonance of a fluid flowing through the orifice passage. The thus constructed fluid-filled elastic mount can provide excellent vibration damping characteristics, which have not been obtained by the above-described elastic mount that utilizes only the elastic body for damping the input vibrations.
In the fluid-filled elastic mount, effective flows of the fluid between the two fluid chambers through the orifice passage take place as a result of relative pressure changes between the two chambers, when the mount receives vibrations in the radial direction in which the two fluid chambers are opposed to each other. Upon application of vibrations in the other radial directions of the mount, however, the fluid-filled elastic mount is not able to provide a satisfactory effect of damping the applied vibrations.
However, it is rather difficult for the fluid-filled elastic mount to provide a sufficient degree of damping and/or isolating effect for the vibrations applied in all the radial directions perpendicular to the axis of the mount. Even if the elastic mount receives vibrations applied in only one radial direction, the installation of the mount on a motor vehicle, for example, must be effected so that the direction in which the two fluid chambers are opposed to each other coincides with the radial direction in which the vibrations are applied to the mount, since the mount exhibits sufficient damping characteristics only for the vibrations applied in that direction. Thus, cumbersome procedures and considerable precision are needed for the installation of the conventional fluid-filled elastic mount.